1. Field of the Invention
The invention relates to a thin film transistor and a method for manufacturing the same, a display device and a method for manufacturing the same, and a television device using the above.
2. Description of the Related Art
A thin film transistor (hereinafter, referred to as a “TFT”) and an electronic circuit using the thin film transistor are manufactured by stacking various types of thin films of such as a semiconductor, an insulator, a conductor over a substrate and then, appropriately forming a predetermined pattern by photolithography. The photolithography is a technique of transferring a pattern of a circuit or the like formed with a material which does not transmit light over a transparent flat surface, referred to as a photomask, onto an objective substrate by utilizing light. The technique has been widely used in the manufacturing processes of a semiconductor integrated circuit and the like.
In the manufacturing process employing a conventional photolithography technique, a multi-stage process including light exposure, development, baking, peeling, and the like are required only for treating a mask pattern which is formed of a photosensitive organic resin material referred to as a photoresist. Therefore, as the number of the photolithography steps is increased, the manufacturing cost is inevitably increased. In order to improve such problems as described above, it has been tried to manufacture a TFT by reducing the number of the photolithography steps (for example, Reference 1: Japanese Patent Laid-Open No. H11-251259).
However, in the technique disclosed in Reference 1, only some of the plural photolithography steps in a TFT manufacturing process are replaced by printing method, and no contribution is made to a drastic reduction in the number of steps. Further, a light exposure apparatus to be used for transferring a mask pattern in photolithography transfers a pattern of under several micrometers to one micrometer or less by equivalent projection light exposure or reduction projection light exposure. It is theoretically difficult, from a technical standpoint, to expose a large substrate which is more than one meter on a side to light all at once using the light exposure apparatus.
As to a thin film transistor which is formed by stacking various thin films, it is important to improve the planarity of a formation region where thin films are formed, so that the respective films are formed with good adhesion and stability. This is because reduction in step coverage or nonuniformity of processing is caused in a thin film when a formation region has poor planarity (for example, Reference 2: Japanese Patent Laid-Open No. 2000-150906).